Explanation: When people get scared, frightened, they sometimes shake because of the fear they feel. A milkshake is a drink that mixes (or shakes) together ice cream and milk (sometimes with fruit or chocolate or …). So, if you shake a cow (which would be really hard to do!) you could get a milk-shake. Or if the cow gets scared it could shake itself and the milk that is inside it thereby making a milkshake. Crazy! It could never happen! That’s why it’s funny!